Characterization of a genomic region encoding the 32-kDa dense granule antigen of Sarcocystis muris (Apicomplexa)

Two subgenomic libraries constructed from Sarcocystis muris total DNA were screened with a cDNA probe, specific for a 32-kDa protein associated with the dense granules. Two clones reacted positively and were isolated, gDG 32/1 and gDG 32/2. Genomic clone gDG32/1 and part of clone gDG 32/2 have been sequenced. The composite nucleotide sequence of these genomic clones comprises 4.34 kb. It contains a 5' region of 2.14 kb, a first coding region (222 bp, exon I), a noncoding region (608 bp, intron), a second coding region (660 bp, exon II), and a 3' region of 693 bp. The upstream region shows a eukaryotic promoter structure and a consensus sequence for the 5' and 3' splicing sites. Thus the open reading frame (ORF DG32) coding for the 32-kDa protein of the dense granules of S. muris cyst merozoites is interrupted by an intron. To our knowledge, dg32 is the first sarcosporidian mosaic gene to be characterized.